Thyristors

Thyristor consists of four layers of silicon in a p-n-p-n structure. Its circuit symbol shows that it is basically a diode, but with an additional terminal, called the GATE.When a small current flows into the GATE (G), this allows a larger current to flow from the ANODE (A) to the CATHODE (C). Even when the current into the gate stops the thyristor continues to allow current to flow from anode to cathode. It latches on.

Thyristors are widely used in applications where DC and AC power must be controlled. These devices are often used to apply a specific amount of power to a load or to completely remove it however, they are also used to regulate or adjust the amount of power applied to a specific load.